1. Field of the Invention
This invention relates to an ink jet recording head, and more particularly to an ink jet recording head for generation of small droplets of ink to be used for an ink jet recording system.
2. Description of the Prior Art
Ink jet recording heads to be applied for ink jet recording systems are generally provided with minute ink discharging outlets (orifices), ink pathways and an ink discharging pressure generating portion provided on a part of the ink pathway.
In the prior art, as the method for preparing such ink jet recording heads, there has been known, for example, the method in which minute grooves are formed on a plate of glass or metal by cutting or etching and then the plate having the grooves is bonded with an appropriate plate to form the ink pathways.
However, in the head prepared by such a method of the prior art, there may be formed too much roughness of the internal walls of lhe ink pathways worked by cutting or may be formed distortions due to the difference in etching degree, whereby ink pathways with good precision can hardly be obtained and the ink discharging characteristics of the ink jet recording heads thus prepared are liable to fluctuate. Also, chipping or cracking of the plate is liable to occur during cutting work to give a disadvantageously poor yield of the production. And, in etching work, a large number of production steps are involved leading to a disadvantageous increase of cost. Further, as the drawback common in the preparation methods of the prior art as mentioned above, during lamination of an engraved plate having formed ink pathway grooves and a cover plate having driving elements such as piezoelectric elements, and heating elements for generating energies for ink jet, the precise adjustment of their mutual position is difficult, thus failing to afford mass-production.
As a new method for producing ink jet recording heads which can overcome these drawbacks, there has been proposed a method for the production of ink jet heads in which ink pathway walls are formed from a cured film of a photosensitive resin on a substrate provided with ink discharging pressure generating elements, and thereafter a covering is provided over said ink pathways, as disclosed in Japanese Laid-open Patent No. 43876/1982.
The ink jet recording head manufactured with the cured film of a photosensitive resin is excellent in that it overcomes the drawbacks in the ink jet recording head of the prior art, namely insufficient precision of the finished ink pathways, complicated production steps and low production yield. However, due to the deficient bonding strength between the substrate having provided ink-discharging pressuregenerating elements thereon and the ink pathway walls made from a cured film of a photosensitive resin, when a photosensitive resin film is employed as the covering over said ink pathway walls, the covering made of the photosensitive resin shrinks on curing, whereby the ink pathway walls are drawn toward the direction of shrinkage of the covering until they are peeled off from the substrate. Even when the bonding strength between the ink pathway walls and the substrate is sufficient, there may be still involved the drawback that the ink pathway walls are drawn toward the shrinking direction of the covering to modify the shape of the ink pathway somewhat is desired. Further, when a cold-setting adhesive, a hermosetting adhesive or a photosetting adhesive is employed for provision of a covering over the ink pathway walls, together with the drawback that the adhesive may flow into the ink pathways to clog it to lower markedly the production yield, there may also be involved the drawback that, due to the difference between the wettability of said pathway to ink and that of the covering, such adhesives affect on the precision of the shot spots of the ink droplets or on the response frequency.